[time-nuts] wwvb weak on east coast especially when the pre-amps under wa...
mblazer at satx.rr.com
Mon May 14 23:23:31 UTC 2012
Here's comparison for various type of conformal coating:
I think there is a type that is 'serviceable' and removable with alcohol.
On 5/14/2012 6:01 PM, GandalfG8 at aol.com wrote:
> The other option of course is to pressurise the box with dry air to ensure
> a positive pressure differential, such that the net flow is always outwards
> at all points, but it's probably easier just to provide a drain hole:-)
> However, whilst a drain hole will prevent the build up of a lake inside the
> enclosure it still doesn't prevent condensation forming on circuit boards,
> and powered circuit boards and condensation don't really go well together.
> As per earlier comments, it's quite difficult to keep any externally
> mounted enclosure totally moisture free, so it's much easier to accept the
> inevitable and allow for it.
> In a past life I designed quite a few circuit boards that were required to
> be fitted in externally mounted vented enclosures, so not a great deal of
> pressurisation there then:-), and I usually specified that both sides
> should be sprayed with a plastic coating following final test.
> I can't remember now exactly what this stuff was called, but it was
> readily available in the UK from both RS and Farnell as an aerosol plastic spray
> that provided a good barrier but was a bit more flexible than the usual MOD
> spec conformal coatings.
> It melted easily under a soldering iron, albeit with a foul pong:-), so
> reworking was no problem, and resisted moisture remarkably well.....
> problem solved:-)
> In a message dated 14/05/2012 23:10:30 GMT Daylight Time,
> arnold.tibus at gmx.de writes:
> The only solutions I think:
> Apply air pressure tight boxes having a breathing hole an the bottom,
> mount the
> box that no rain and water can penetrate from the top or sides. If the
> hole is big enough,
> eg. 2mm, no pressure difference is possible and no pumping effect will
> (If the hole is too wide, small animals may penetrate).
> when using a pressure tight box, it must be stiff and sealed to
> withstand under all
> temperature conditions more then 1 bar/ 100 kPa. Do not forget that all
> throughs must be of real hermetic type, normal coaxial connectors are
> not tight!
> Don't route cables directly in, because no cable braid or mesh is vapor
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